Removing Moss, Mildew, Fungus and Associated
Stains on Roofs

Roof cleaning is a topic that draws yawns in New England but causes shudders and
screams of agony from Florida and points south, where vegetable life seeks
world domination! How do we keep that "fungus among us" under control.
(Graphic left courtesy Spray and Forget
mildew and moss remover.)

Since starting on a quest for the ideal method of cleaning fungus and algae
from roofs, I have contacted dozens of individuals and companies. Some of my readers came forward
with suggestions and a few companies also supplied information helpful to this
research.

For the purposes of this article, the terms "mildew", "fungus", "algae" and
"moss" are interchangeable... even though their mothers' might object!

Chlorine bleach cleaning mixtures are one option...

If you've had experience with mold and mildew in the home, you know the best mildew remover is
chlorine bleach. But outdoor, heavy duty cleaning
usually calls for more heavy-duty mixtures such as TSP and chlorine bleach (see the TSP
page for more details), or specialty additives such as Jomax from Rustoleum, which combines a cleaner with a bleach activator.

How to use bleach mixtures on your roof...

The following procedure is for bleach-cleaning only using JOMAX.
(Other cleaning options are mentioned later in this article.) If JOMAX
is not available in your area, use a
TSP mixture with bleach added.

Bleach mixtures can injure sensitive plants. Because
it is difficult to totally protect them from the mix, spray
them down with clean water before applying the mix and immediately after,
whether you cover them or not!

Using a plastic pump-type garden sprayer, thoroughly soak the affected
area with your choice of chemical. Allow it to sit for at least 5 minutes.

Wash off all dirt and fungus residue. NOTE:
Though powerwashing was recommended for years, the industry has moved towards low-pressure
cleaning due to
evidence of permanent asphalt shingle damage caused by high-pressure powerwashing.

Allow the roof to dry thoroughly. Inspect the roof for any remaining fungus... if it is
slimy, or any sort of residue comes off on your hand, repeat the above steps.
You must let the roof dry before a second application of mix. A second
application of cleaner will not have its full effect on a damp surface!

If you think it wise to leave the bleach-brew on the roof longer than the
recommended time, think
again! As mentioned earlier, long term exposure to bleach can damage most any surface, and your
roof is no exception. However, this piecemeal approach is the likely
to cause the least damage.

Problems with using bleach on asphalt roofs...

There is some concern regarding the use of chlorine-based products
on asphalt roofs. Household bleach can damage asphalt
due to its high sodium content. Apparently, the sodium causes an
electrochemical reaction that reduces the elasticity of the asphalt leading to stiffness, brittleness and curling of the shingles. (I suffer from two of
those symptoms myself!)

Thankfully, there are some "killer" alternatives to bleach...

1) Sodium hydroxide products are NOT recommended!! A chemical alternative to bleach uses the
antifungal agent sodium hydroxide... also known as lye. Lye-based
products appeared on the market a few years ago, but turned out to be even more
dangerous to use than bleach! Even at low
concentrations, permanent damage could be done to the roofing, possibly even
dissolving the roofing nails!

Fortunately, most lye-based products have
been removed from the market.

2) Here are a few bleach-free chemical treatments that can help keep
fungus under control:

Spray and Forget is a new product that offers a long-term solution
to fungus problems. It is sprayed on and allowed to dry without rinsing.
Though it is slow-acting when compared to bleach solutions, it can prevent
mildew growth for years! If you want to see quick results, you can do a
one-shot bleach cleaning. Rinse thoroughly, allow to dry and then apply
Spray and Forget according to the instructions.

Moss Out! comes in a number of formulations, one specifically for
roofs and others designed to remove and/or inhibit moss and fungus growth on
siding, masonry surfaces and even lawns. Their formulae use tried and
true zinc compounds that linger on surfaces to provide continuing protection
from fungus regrowth.

Preventing reinfestation... zinc strips are one option

If you wish to prevent reoccurrence of fungus, think zinc! Zinc
strips (left) have been used for many years as an algae preventative. StainHandler.com offers sets of 3' zinc strips, which are
attached near the peak of the roof. When it rains, a slight amount of zinc
dissolves from the strips and coats the roof, inhibiting algae and fungus
growth.

Would you believe... fungus-resistant shingles??

Yessiree... the 3M Company
has developed an additive for asphalt roofing
shingles using copper granules. This unique advance in shingle technology
gives long-term fungus protection for the entire roof. They
call it the AlgaeBlock system. You can find more information on
these special roofing shingles
HERE.

3M is not a manufacturer of asphalt shingles, just the granules. However, at the time of this writing they do list a
number of companies that are producing shingles meeting their specifications.